1.
According to the data in Figure 8.4, the first labeled mitotic cells appear about 4 hours after a labeling period ends. Labeled cells are then observed in mitosis over a span of 6–8 hours. From these data, researchers concluded that S phase lasts 6–8 hours and G2 lasts about 4 hours. Explain their logic.
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2.
Sketch the phases of mitosis, listing the major events that occur in each phase. Identify at least two events that must be completed successfully for daughter cells to share an identical complement of chromosomes.
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3.
What are the consequences for the cell if the G1 checkpoint fails? Answer the same question for the G2 checkpoint and the metaphase checkpoint.
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4.
Explain how cell fusion and microinjection experiments supported the hypothesis that specific molecules are involved in the transition from G2 to M phase and from G1 to S phase.
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5.
Why are most protein kinases considered regulatory proteins?
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6.
Why are cyclins called cyclins? Explain their relationship to cyclin-dependent kinases and to growth factors.
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7.
Early detection is the key to surviving most cancers. Why?
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